1. Field of the Invention
The present invention is directed to a radiological diagnostics system of the type wherein a radiological image of an examination subject, who has been injected with a contrast agent, is generated.
2. Description of the Prior Art
For many radiological investigations, it is desirable to trigger the imaging exposure, after the injection of a bolus of contrast agent, at exactly the time of arrival of the bolus of contrast agent in the organ or body region of interest, in order to achieve optimum contrast and/or to completely image the bolus if the examination is a dynamic examination. A problem in obtaining such exact triggering is that the passage time of the intravenously injected bolus (usually injected into the vein of an arm) through the right atrium, right ventricle, circulation through the lungs, the left atrium and left ventricle and to the organ of interest varies greatly from patient to patient. In addition to being dependent on parameters such as the heart rate, which can be relatively easily acquired, this passage time is dependent on other parameters which cannot be reliably monitored. A current problem is to obtain such synchronization in the context of spiral computer tomography, wherein complete organs or body sections are to be examined in the shortest possible time, and thus exact synchronization of the imaging with arrival of the contrast agent bolus is necessary. Frequently, a portrayal of blood vessels (CT angiography) is also desired. The triggering problem, however, is present in all examinations which require an injection of a contrast agent.
The above problem has not been exactly resolved, but has heretofore been approximately resolved by relying on the experience of the physician or radiologist. The examining person acquires the appropriate experience through examination employing transillumination monitoring, for example in digital subtraction angiography. Recommendations for estimating the passage time after injection of the contrast agent bolus, primarily dependent on the pulse rate, have been developed on the basis of such examinations and other fundamental studies. Such procedural rules, however, provide only approximate suggestions, resulting in the imaging exposure being triggered too early or too late in many instances, particularly in the case of examining personnel with less experience. If the x-ray imaging is triggered prematurely, this results in an unnecessary increase in the radiation dose to the patient. If the x-ray imaging is triggered too late, the image of the bolus is not completely acquired, which can mean that the results of the examination are not useable, and the entire examination must be repeated. The problem does not lend itself to a procedural protocol which is applicable in all examinations since, for example, the circulation parameters of a patient can change very rapidly.